This invention relates to an electric switchgear comprising at least one switching element which is a semiconductor with a temperature-dependent resistance and which is arranged in a liquid-tight housing, from which contact tabs project of the switching element.
In order to produce a switching element of the initially mentioned type, it is known from German Patent Document DE 37 03 465 A1 to provide a mounting body which holds electric contacts with a semiconductor arranged in-between and around which, together with the contacts and the semiconductor, plastic material is cast. The plastic material will then form the housing including a plug receiving device.
It is also known, from German Patent Document DE-G 6 610 339.7, to coat a semiconductor provided with electrodes with a thin heat-resistant plastic layer to which a metal coating is applied by currentless metal deposition and subsequent electrodeposition. The semiconductor with the electrodes is held by connecting wires in a ceramic insulating body which is partially covered by the plastic layer and also by the metal coating.
An object of the invention is to provide a switchgear of the initially mentioned type which is simple and inexpensive to manufacture and permits a good heat transfer to the semiconductor or semiconductors.
This and other objects are achieved in that the housing is joined together from a metal cap and a closing element made of plastic, in that the contact tabs are fitted into recesses of the closing element, and in that the metal cap and the closing element are connected with one another by a joining element made of plastic which is cast on the outside and which encloses the edge of the metal cap and encloses the closing element at least partially.
In the switchgear of the present invention, the metal cap and the closing element made of plastic, together with the semiconductor or semiconductors and the contact tabs, form a constructional unit which can be preassembled and which is then completed to form the finished switchgear by the molding-on of the joining element. The joining element holds the individual elements of the subassembly securely together and provides a liquid-tight connection. The metal cap, in whose area the semiconductor or semiconductors is/are situated, permits a good heat transfer so that a fast response to the respective temperatures is ensured.
In certain embodiments of the invention, the contact tabs are fixed in the joining element. The contact tabs, which at first are fitted into the closing element only relatively loosely, are securely held by the cast-on joining element so that, in particular, connections are possible that can be plugged in.
In certain embodiments of the invention, the joining element surrounds the areas of the contact tabs by a surrounding web which is constructed as a plug housing. In these embodiments, a plug housing is therefore created at the same time by the molding-on of the joining element.
In certain embodiments of the invention, the joining element has a ring collar serving as a holding device for the switchgear.
In certain embodiments of the invention, the interior space between the metal cap and the closing element is filled with a medium at least in the area receiving the switching element or elements, this medium having a higher thermal conductivity than air. Thus, the rate of response of the switchgear is improved further. Advantageously, it is provided in these embodiments that the interior space is filled at least partially with a hardening resin. This ensures that the switching elements are securely fixed in the interior space so that the switchgear will not be damaged even in the case of shocks and vibrations.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.